Many types of natural and synthetic polymeric materials are incorporated in aqueous systems for the purpose of providing a thickening or gelling effect.
Illustrative of such thickening agents are natural gums and resins such as starch, gum arabic, modified starch products, dextrins, sodium alginates, tragacanths, and the like. Synthetic materials employed as thickening agents include carboxymethylcellulose, polyvinyl alcohol, polyacrylamide, polyacrylic acids and salts thereof, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyvinylpyrrolidone, polyvinylmethylether, polyethyleneoxides, and copolymers of polyvinylmethylether and maleic anhydride. Thickeners of the polyelectrolyte type include synthetic polymeric water-soluble polymers such as the sodium polyacrylates as well as the copolymers of various acrylates, such as are described in U.S. Pat. Nos. 2,798,053; 2,883,351; 2,956,046; 3,035,004; 3,436,378; 3,915,921 and 4,167,502.
Water-soluble polyelectrolyte copolymers employed as thickeners include those esters prepared by the esterification reaction between the acid anhydride groups of a copolymer of an alkylvinylether and maleic anhydride with the terminal hydroxyl groups of a nonionic surfactant of an alkylphenoxyethoxyethanol polymer. The resulting water-soluble polymer is a partial ester which contains free acid groups suitable for subsequent neutralization with a basic material, such as an amine or a metal oxide or hydroxide.
Other thickening agents are carboxylic acid polymers made by copolymerizing acrylic acid with a small amount of a polyallyl polyether of a polyhydric alcohol, e.g., polyallyl sucrose. Such polymers are insoluble in water. The alkali metal salts of which swell in water to form gel like compositions.
Print pastes always contain a thickening agent (besides dyes, binders and other auxiliaries) which provides them with the required degree of viscosity. The thickening agent should be compatible with the conventional components of a textile print paste and should not impair either the dye yield or the fastness of the print. In the case of prints which have been prepared with print pastes containing conventional thickeners, they are often sensitive to squeezing so that a lower dye yield is obtained.
Also, some polyacrylic acid thickening agents of the prior art have generally been associated with the production of harsh hands when they have been used for thickening of impregnating materials for textiles, such as pigment-printing and dyeing compositions. They are also characterized by difficulty in formulation and impairment of water-resistance of the textile or other article treated with compositions containing the known thickeners of this type.
Improved results have been obtained by the development of aqueous emulsions of copolymers of acrylic (or methacrylic) esters with acrylic (or methacrylic) acid more or less reticulated. These emulsions dissolve well in water at a nearly neutral pH value (pH 6-7) to yield appreciable viscosities. These improved products are advantageous due to the possibility of thickening in situ from a fluid emulsion containing 25-40 percent of polymeric solids. However, it is not practical to obtain the polymeric solids in the form of a dry powder, so that they must be stored and handled as aqueous dispersions or solutions. In addition, the thickening agents made by these processes are not as efficient as other prior art thickening agents and require excessive amounts to obtain good results.
Further, thickening agents which contain 10-40 percent acrylic acid or methacrylic acid do not permit the coloristic effect of pigmentary printing pastes to be sufficiently emphasized. In order to avoid obtaining prints which are too dull, the least concentration of thickening agent is employed. In this case, a poor retention of the aqueous phase occurs, which leads to spreading or running effects, and results in prints with diffused outlines.
U.S. Pat. Nos. 3,426,004; 3,817,949; 3,878,151; 3,894,980; 3,978,016; and 4,138,381 are representative of more recent developments which have endeavored to overcome one or more of the disadvantages associated with the manufacture and use of polyacrylic acid type of thickening agents.
Accordingly, it is an object of this invention to provide a novel polyacrylate interpolymer which is adapted for use as an improved type of thickening agent.
It is another object of this invention to provide a high viscosity liquid composition which is adapted to perform as an improved printing paste medium.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.